1. Field of the Invention
This invention relates to an electric wire holding structure for a connection box to protect the joint portion of a flat cable and terminals against external tensile force loaded on the flat cable, juxtapositionally combined in one with a plurality of electric wire main bodies and connected to terminals in a connection box body such a joint box body or the like and clamped at the connecting portions of the flat cable by the joint box body.
2. Description of the Related Art
FIG. 5 is showing one embodiment of an electric wire holding structure of a conventional connection box (joint box).
A joint box body 43, made of synthetic resin, includes a base 41, a cover 42 and pressure contact terminals 44 made of a conductive metal inside. Intermediate position along the length of electric wires 26 is connected to the terminal 44 and the electric wire 26 extends out of gaps between the base 41 and the cover 42 and is formed into wave-like shape by three positions of a rib 24 provided on the base 41 for strain-relief, a rib 25 provided on the cover 42 for strain-relief and a wire opening 45 to protect joint portions of electric wires 26 and terminals 44 against external tensile force loaded on the electric wires 26 by cutting off transmitting the tensile force to the joint portion.
A joint box 46 is provided mainly with the joint box body 43 and the pressure contact terminals 44, connecting a plurality of the electric wires 26 reciprocally inside the joint box body 43. The juxtapositionally terminal combined type with the same number of terminals 44 as the joints of the electric wires 26 may be used.
The electric wires 26 is round type insulated electric wire which is round shape cross section conductive wire, covered with insulating resin to have round shape cross section. The pressure contact terminal 44 consists of a blade (not shown) cutting the insulation of the electric wires 26 and a slot (not shown), continuous to the blade, holding and connecting the conductive portion of the electric wires 26. Instead of the pressure contact terminal 44, a laser beam welding terminal or a crimp contact terminal which is crimp-contacted at the conductive portion, removed the insulation of the electric wires 26 at intermediate portion on the length direction, can be used.
The joint box body 43 is formed in thin wall thickness rectangular solid shape and the base 41 and the cover 42 are jointed with thin hinges (not shown) on the side of each edge to be open-close free as an example. The ribs 24 (strain relief) as a part of the base 41 are provided at the both of front and back sides of the pressure contact terminals 44, mounted on almost center of the base 41. The ribs 25 (strain relief) are provided closely at outer side of the ribs 24 on the cover 42. Each ribs 24, 25 extends long along radius direction of the electric wires 26 to form juxtaposed plural electric wires 26 in wavelike shape simultaneously.
The wire openings 45 are provided closely outer side of the ribs 25 on the cover 42 in the both of front end and back end side of the joint box body 43. In this description, front and back are defined along the length of the electric wires 26. The wire openings 45 are to become round shape openings to be combined by each semicircle opening, formed opposite each other on the perpendicular walls of the base 41 and the cover 42 when the cover 42 closed.
After connecting the electric wires 26 to the terminals 44, owing to close the cover 42 to the base 41, the electric wires 26 are pushed down to the bottom surface of the base 41 by the ribs 25 on the cover 42 and are formed in clank shape between the ribs 24 on the base 41 and the wire openings 45. Therefore, very stronger tensile force, loaded on the electric wires 26, enlarges friction force between the electric wires 26 and each ribs 24, 25. Then, electric connection is kept in good condition because the loaded tensile force on the electric wires 26 is caught by the each ribs 24, 25 and transmission of the tensile force to the joint portion of the electric wires 26 and terminals 44 is prevented.
This structure cannot be applied only on the joint box 46 but also on connection boxes, such a pressure contact connector which includes with base portion, cover portion and pressure contact terminals.
In the electric wires holding structure of connection boxes by ordinary skills, forming the electric wires 26 in wavelike shape by ribs 25, 24, projected upwardly and downwardly on inner surface of the joint box body 43 for strain relieves as tension relaxing parts, has issues to require enough rooms inside and bigger size of the joint box 46.
Further, very strong force for closing the cover 42 required to push the electric wires 26 and form the wires in radius direction of the wire with ribs 25 makes assembling of the joint box 46 troublesome. Forming a plurality of electric wires 26 simultaneously in the joint box is more troublesome.
Adjusting the projecting height of ribs 24, 25 is required as lower height rib is for thicker wire and higher height rib is for thinner wire, various kinds of joint box body 43 are necessary for each size of the electric wires 26. It makes a number of kinds on the joint box body 43 increased and manufacturing and administration costs push up.
This invention has been accomplished to overcome the above drawbacks and an object of this invention is to avoid increasing outer size and inner room size of connection boxes such a joint box or the like and to provide an electric wire holding structure of a connection box, easily assembled as the cover can be easily closed and unnecessary to change the connection box body for each electric wire size.
In order to attain the objects, regarding a connection structure having electric wires inserted through a gap between a base and a cover of a connection box body and terminals connected to the electric wires within said connection box, the connection structure comprising opposed projections for clamping connecting portions between each electric wire main body of a flat cable, which constitutes said electric wires, being provided at each end of wire lead-out side of said base and cover, whereby said connecting portions of said flat cable are fixed by clamping with the projection.
In the above structure, a flat cable by connected plural electric wire main bodies juxtapositionally can be clamped strongly in a connection box body. Therefore, the reliability on electric connection of a flat cable and each terminal is improved, as each projection of the base and the cover holds the tensile force of the flat cable and eliminate the affection of the tensile force to a joint portion of electric wire main bodies and terminals, when a strong external tensile force loaded on the flat cable.
Further, the inner room size of the connection box body can be shrunk and the connection box size can be miniaturized in the length and radius (vertical) direction of the electric wires because conventional ribs for pressing electric wires is not required and forming the electric wires wave-like inside the connection box body is not required. Manufacturability to close the cover, in other words, manufacturability of assembling the connection box is improved because disuse of forming the electric wires with sharp angle (close to 90 degree) and clamping with large deformation at the flat connecting portions of the flat cable as usual makes the force of closing the cover smaller. Even if the diameter of an electric wire main body changed, the pressing operation of the connecting portions is done by common method and the connection box body can be common use, because of pressing the connecting portions for connecting electric wire main bodies by the projections instead of pressing electric wire main bodies. This allows reducing manufacturing cost and administration cost of the connection boxes.
Advantageously, each of said projections is formed between respective juxtaposed openings for electric lead-out wires. In this structure, the flat cable can be pressed uniformly at plural positions along juxtapositional direction of electric wire main bodies with the same interval and this allows stronger and more stable holding force for the flat cable and then connection area of the terminals can be protected reliably against the tensile force on the flat cable.
Advantageously, each of said projections has flat surface at the top end for pressing connecting portions. In this structure, each flat surface at the top end of projections contacts closely the upper and down surfaces of the each connecting portion of the flat cable without gaps between the connecting portions and the top ends. Then, without slipping between the flat cable and the each top ends, pressing the flat cable with constant pressure by each projections along juxtapositional direction of the electric wire main bodies can react on strong tensile force in the whole width of the flat cable when the tensile force loaded on the flat cable.
Advantageously, one of the projections is formed into convex shape at its top end while the other projection is formed into concave shape at its top end. In this structure, the convex section of the upper-side projections deform the thin connecting portions of the flat cable to push the connecting portions into the concave section of the down side projections and the connecting portions fit into the concave sections. Therefore, the friction force between the connecting portions and the projections is increased and then the holding force of the flat cable is increased to react against stronger tensile force on the flat cable.
Advantageously, connection structure wherein said convex sections and said concave sections are formed into V-shape or semicircular shape. In this structure, as the connecting portions of the flat cable are deformed to fit tightly into the concave sections by V-shape convex and concave sections of the top ends of projections, the holding force of the flat cable is increased more and reacts strongly against the tensile force on the flat cable. Furthermore, clamping the connecting portions of the flat cable with semicircular shape concave and convex sections prevents to damage the connecting portions and then extends the life of the flat cable.
The above and other objects, features and advantages of this invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings.